In enclosed environments, whether underground, under water, at high altitude, or even in outer space, gas distribution systems often consist of a pressurized tank of gas that is released to the ambient environment through a small output nozzle. The nozzle can have a diameter of less than one twentieth of one inch. Flow of the gas, e.g., Nitrogen or Oxygen, can be driven by an internal pressure inside the tank of 100 pounds per square inch (psi) or more while exiting to an external pressure around atmospheric pressure, between 0 and about 14.7 psi. This pressure difference will create a supersonic flow and cause a shockwave breakdown, which creates a whistling sound as the gas leaves the nozzle. In the range most potentially audible to human ears, 65-8000 Hz, this sound can reach a volume of 80 dB or more.
Such a noise level is distracting to anyone near the nozzle. Moreover, if not reduced at the source, the noise can be transmitted great distances to annoy others in the enclosed environment. Thus, efforts have been made to reduce the noise levels associated with a gas distribution system at or within a short distance from the noise sources in the system. Such efforts have not been entirely successful.
Previous systems have employed techniques such as mufflers, where baffles extend into the path of the sound waves, in an effort to reduce noise. Upon contact with the baffles, the sound waves lose some of their energy, which the baffles dissipate through vibrating. However, the exchange of energy with baffles is not very efficient; it is difficult to position baffles so that they will be able to help absorb sound energy in all directions; and it is also difficult to vary the sizes of the baffles so that they can interact effectively with sound energy across the broad range of audible frequencies. Thus, mufflers have not been that effective at reducing noise, particularly at the higher frequency end of the audible range, about 1250-8000 Hz which, unfortunately, is the portion of the range that is most annoying to the human ear.
Accordingly, a need has existed for reducing sound energy more effectively and immediately at noise sources such as those that are typically found in gas distribution systems.